SPECIAL REPORT

YOUR E-MAIL ALERTS

(CNN) -- Pets outnumber people in the United States by about 60 million, with furry, feathered and scaly inhabitants numbering about 360 million, according to the pet industry.

"That's a lot of mouths to feed," said Bob Vetere, COO and managing director for the American Pet Products Manufacturers Association.

In the decade from 1994 through 2004, the amount of money spent on pet food, pet supplies, veterinary visits, medicines, live animals and services, more than doubled from $17 billion to $34.2 billion, Vetere said. In 2005 alone $36.3 billion was spent.

An increasing percentage of that money was spent on services that used to be reserved for people: massage therapy, spa treatments, couture clothing and gourmet food.

"Now you've got the Marriots, the Ws and the Westins where you can bring your pet along, and they've got room service," Vetere said. One of these pet-friendly hotels "will bring you, for $19.95, tenderloin in a special souvenir dish with bottled water for your pet, and a bed," he said.

Ancient relations

Humans kept pets as long as 4,000 years before livestock was domesticated, according to Melinda Zeder, director of the archaeobiology program at the Smithsonian Institution.

"There are dog burials in ... present day Israel and Jordan that date back to about 14,000 years ago," Zeder said. "Dogs are felt to be the earliest animal domesticates, probably drawn as wolves to human encampments."

Burial evidence of cats as pets dates back 8,300 years, roughly 4,000 years before the ancient Egyptians started depicting cats on tomb walls, she said.

But as humans domesticated cats and dogs, they selected traits that over time favored lack of aggression. These docile traits led to a number of evolutional, physical changes in dogs.

"Things like lop ears and piebald (spotted) coats are things you see in domesticated animals that you don't see in wild animals," Zeder said. "But another factor that comes in with selection for lack of aggression is greater playfulness, more sort of puppy or juvenile type behaviors."

Dogs, like juvenile wolves, she explained, have a smaller snout, jaw, teeth and cranial capacity than their adult wolf ancestors.

"The most striking is a change in the configuration in the skull and a reduction in the cranial capacity," Zeder said, likening the change in brain size to dogs becoming less intelligent as they became domesticated.

'Looking for love'

Thousands of years later, humans are still looking for these baby-like qualities in dogs, but for different reasons.

Matthew Margolis, a professional dog behavior therapist and animal aggression expert from California, asks his clients why some of them get dogs, especially little dogs. Their response, he says, is, "Well, my children have gone from the home. I'm lonely. I want something to love." The response from young people without families often is that they want a puppy to raise before raising a child. This anthropomorphism results in the last trait anyone wants in a dog -- aggression.

"Uncle Matty," as Margolis is known on his PBS show, "Woof! It's a Dog's Life," said dogs start to bite, growl, bark excessively and fail to become house-trained because their owners neglect to train their dogs and don't act like responsible owners.

"That's why you have so many problem animals," he said. "You can't just bring a dog home. Love is not enough. Love will never change a bad behavior."

There are 5 million dog bites reported each year, resulting in $400 million in legal claims, according to Margolis, who often testifies in pet-dispute court cases.

"The problem is, people are looking for love," Margolis said. "And you wouldn't believe how many people get bit by the family pet."

Bonnie Beaver, past president of the American Veterinary Medical Association and faculty member at Texas A&M University's College of Veterinary Medicine agrees.

"People are thinking of their animals as four-legged humans and not understanding what normal dog or cat behavior is and what the true behavioral needs of the dog and cat are," she said. "Dogs, if we look at the wolf model, would normally spend 20 hours a day with members of their pack. Now we are their pack, and we leave for 10, 12 hours a day and now the dog is alone. And we wonder why they get destructive and develop separation anxiety. Cats would normally be out roaming, and ... to warn other cats they would spray urine. We don't appreciate urine to be sprayed inside the house, but that's a normal cat thing," Beaver said.

The perks of modern life

While modern man's emotional needs may have compromised pets' animal instincts, the health of animals has reaped the benefits of human technological advances.

Beaver cites the high quality of pet food, vaccines, chemotherapy and surgical techniques for extending the life of pets.

"Thirty years ago in the U.S., the average age of a dog was 4 years; the average age of a cat was 3 years," she said. These days the average lifespan of a dog is between eight and 12 years, Beaver said.

According to the APPMA, Americans spent $14.7 billion on pet food and treats in 2005. With a wide scope of options, owners can choose to buy food that best fits their pets needs, from natural and organic to vitamin-enhanced and diet formulas.

"Anything that's a trend in human foods, within four to six months it will be a trend in pet food, too," Vetere said.

Modern insight into ancient animal diets is improving pet food. By re-examining cat diets, for example, food manufacturers are able to create a more balanced product.

"Cats and dogs used to eat leftovers from humans, which isn't necessarily bad. But every species of animal has its own nutritional needs," Beaver said. "When you think of a cat you think of them eating a mouse," she said, explaining that a leftover piece of muscle meat does not have the same nutritional value as a mouse, whose body also offered bone and digested vegetables.

An alternative healthcare is holistic treatment. Less-traditional care methods are becoming more popular, Beaver said, "paralleling what's happening in human medicine." Treatments like chiropractics, acupuncture, herbal medicine and massage all are available for pets these days, although they are not all scientifically proven methods of treatment.

M. Spencer Newman, a veterinarian in Marietta, Georgia, whose practice is limited to treating pets with mobility issues, says holistic treatment tries to "stimulate natural processes within the animals to keep them healthy and restore health as opposed to using drugs as a first choice."

Pet owners' spending is not limited to the basics. The APPMA found in its National Pet Owners Survey that 27 percent of dog owners and 13 percent of cat owners buy their pets birthday presents, and 55 percent of dog owners and 37 percent of cat owners buy their pet holiday presents.

Why do humans dote on pets to the tune of billions of dollars a year? Pet owners report it's because of the bond with their animals, whom they may refer to as their best friend, a companion or a member of their family.

"Animals give you unconditional, unrestricted love," Margolis said.

Of his golden lab, Dakota, Vetere said: "I can sit and talk to him and tell him any problem I have, and he just sits there with his tongue hanging out, smiling at me, just waiting for me to finish. It's like, 'OK, you feel better now? Let's go outside and play.' "